Archive for the ‘Green Energy’ Category

Competing with Tesla


Tesla had an early lead on all battery vehicles when it secured a Department of Energy loan (repaid early with IPO money) in 2006 claiming that it would use new battery technology. At that point, Tesla already had VC funding and partner funding with Daimler and with Toyota. Tesla started with a well-known strategy of high end vehicles and then moving towards mid-range BEV’s in the $30-50k price range. Thus, comparisons with Tesla are inevitable for any electric vehicle (EV). These comparisons are also valid for a future fuel cell vehicle (FCV) for that matter, but I’ll focus here only on battery only BEV’s. I read somewhere that Elon Musk doesn’t worry about the competition, because his operating tactics are to lead with Tesla’s models in every category of Tesla competition.

If the prospect is deciding between an EV or an internal combustion engine (ICE) car, then a classic auto company might not lose a sale if the prospect decides on an ICE or even a hybrid rather than an BEV. Of course, essentially all of the classic auto companies are going to offer EV’s in the fullness of time. Ford for example, in January 2018 announced it would invest $22 billion by 2022 and have 40 EV’s in its product line (16 pure battery electric vehicles (BEV’s = no engine), and the rest hybrids.) If the prospect has decided on a BEV, then here are 10 “customer visible” points of competition for a BEV purchase:

  1. Beauty, style, sunroof, smooth ride (note Consumer Reports thought the ride of a Tesla was “stiff”, quality: exterior and interior, excellent detail, ability to add a roof-rack or a bike rack, place to hang clothes, minimalist design, console, interior space (storage, #passengers, seat size and comfort), passenger TV (movies, and games), …). Owners of BEV’s from all the classic luxury brands as well as new ones such as Fisker, Rivian (backed by Amazon and now focusing on electric pickups and SUVs), and Karma, will argue for the external beauty of their models. The argument around beauty inside the vehicle seems quite open. For example, some like all controls via the center console screen (a la Tesla), while other like distributed controls (a la Volvo’s Polestar 2). Seat comfort is personal; try all the seats and imagine sitting in them for a long trip.
  2. Price (after rebates, tariffs, etc) of a loaded car, including accessories, software updates, home charging station. Warranties, especially for battery packs, must be factored into total cost of ownership. Different packages of options and accessories can, of course, define different models with different price points. Getting a detailed breakdown of Cost before markups and rebates to get the final Price for each model requires a detailed bill of materials, supply chain analysis, manufacturing cost, etc. One big issue on Cost is the cost of the battery packs. They are currently (January 2019) running around $200 per kWh. Tesla has a (seemingly always slipping) goal of getting this under $100 per kWh by 2026 or earlier, which, for its 80 kWh battery packs, is a significant savings. A vexing problem is the limited worldwide supply of cobalt, which should drive battery prices up as cobalt becomes more and more scarce. Worse than the Cobalt supply in the 2019 shortage of battery manufacturing capacity. Any BEV company that has secured its supply will have a huge advantage. The Bloomberg New Energy Finance (BNEF) predicts that the total cost of ownership, including initial price, fuel, repairs, 5 year battery pack replacements, etc. of BEV cars will be less than the comparable ICE cars by 2022. How about cost in the first year? Cf. Cost is also related to where cars and parts are manufactured. Some prospects will want their cars to be mostly “made in America”. Additional Gigafactories to manufacture 2170 cells will be needed. Sites in China and Germany have been proposed. Another point of competition will be around retail stores and developing customer relationships both for service and hand-holding in general. Tesla is moving more to on-line sales and the elimination of its retail stores to drive costs down. It would seem that the larger auto manufactures with stores whose costs can be spread across multiple types of cars (ICE, Hybrids, and BEVs) may have an advantage. Exactly how Tesla will deal with the service side of its retail stores is unclear and will certainly be another point of competition.
  3. Range and battery capacity. Most of the time an EV prospect wants to know range (at various speeds); in fact all BEV owners want to avoid “range anxiety”. Cf. For Tesla and also , and for Fisker E.g. Los Angeles to Las Vegas is a little under 300 miles typically at 80mph through the desert, and Los Angeles to San Francisco is a little under 400 miles at 65-70mph. While needing a charge close to San Francisco where there are lots of charging stations isn’t a big deal, needing one in the desert outside of Las Vegas would be most annoying. Finally, most (all?) BEVs also have some form of regenerative braking, which allows the motors to brake by running with the supply to the rotor cut off and the supply only given to the stator. Thus, the rotor constructor cuts the stator magnetic field to produce a voltage which is fed back to the batteries. This extends the battery capacity (i.e. range) by 10 to 15% by converting kinetic energy (and slowing down the vehicle) to electricity. Bottom line: batteries are a big deal, and the battery management system is an even bigger deal!!!
  4. The ICE driver is accustomed to having a plethora of gas stations, and being able to fill the gas (or diesel) tank in a few minutes. The BEV owner wants something comparable. It’s going to take a long time for the infrastructure of charging stations to be as dense as today’s gas stations, but the technology for fast charging times is coming quickly. Charging times depend primarily on the power characteristics of the charging station and secondarily on the battery type and internal connections. Battery packs based on the 2170 cell are purported to be an improvement with faster charging characteristics. Typically home charging stations are very slow. Even today’s 50 kw charging stations are much slower than next generation 350 or 450 kw chargers. BEV owners want, therefore, a large number of fast charging stations (incl adapters and protocols) not only near home and work, but also along any travel route planned. There is an interesting company, ChargePoint, that builds and deploys charging stations, whose business goal is to dominate the charging station business. There is a similar company, GreenWay, in Eastern Europe. Note that non-Tesla BEVs need a special smart adapter to use Tesla charge stations. Conversely, a Tesla needs an adapter to use a “standard” charging station. Tesla provides a J1772 adapter with each Tesla vehicle. Note that Tesla has given up on battery pack swaps. Cf. Electrify America, if you got screwed by Volkswagen’s cheating. For China sales, Tesla has announced a charging port that is compatible with the Chinese charging stations which have China’s standard, but will use the Japanese CHAdeMO standard in the future. Any U.S. company wanting to sell EV’s in China will have to do the same and provide charging ports for both standards.
  5. Service/Maintenance Service begins with the first customer contact: helpful and knowledgeable sales staff, help with all options, help with deposits and warranties, delivery dates that don’t slip, etc. Maintenance includes: general reliability, speed/cost, incl warranty, e.g. for drive-train or battery pack replacement, need for regular service (e.g. lubrication). Key: #trained and equipped, reasonably priced, servicers, incl mobile (concierge) servicers; excellent MTTF & MTTR incl battery packs. A big competitive issue to investigate is the availability of parts. A dealer probably has the best inventory of parts outside of the factory, and a mobile truck the worst. A licensed third party shop such as the nationwide network The Hybrid Shop for Fisker may or may not have parts and may or may not be able to get them via fast (ideally, overnight) shipping. If the servicer needs to order a part from the factory, it could be a month or more to get it. [Tesla customers “fume” about such service delays (SF Chronicle, July 2018, LA Times Feb 2019)]. Phone support is also a useful point of comparison, especially for new BEV owners.
  6. Safety: front, rear, and side collision passenger protection (crumple zones), air bags, National Highway Traffic Safety Administration (NHTSA) top rating, excellent braking. Low center of gravity = roll-over protection; BEV companies should excel here by keeping heavy battery modules low. BEV batteries must be free from fire, explosions, leaks, melting during charging, and must be protected from crashes or roll-overs. They should have excellent braking, both regenerative and friction. Compare the distance to go from 60 mph to zero. They should have excellent emergency handling.
  7. Acceleration: 0-60 mph times should be excellent, but the competition here is not with ICE cars, but it is among the BEVs, with 0-60 times going from 9+ seconds (slowest) to 1+ seconds (fastest). The Tesla Roadster goes 0 to 60 in 1.9 seconds.
  8. Handling (how to measure?) Low center of mass, weight, wide wheel base, best tires, …all favor BEVs in general. There is nothing like getting a prospect into a BEV and trying a few turns! I should note that so far, Tesla dealers do not offer test drives to non-committed prospects. Try taking test drive cars over bumpy roads. Test any all-wheel drive (AWD). Can it tow? BEVs should be quiet, how quiet? How comfortable are the seats, especially on long rides?
  9. Environment: All BEVs are environment friendly; no oil or petrol needed. For someone concerned about zero exhaust pollution, a BEV should win over a hybrid. While lubrication does use carbon based products [transaxle, motor, CV joints, gears, doors, windows, wheel bearings need minor lubrication (sealed bearings not withstanding), this lubrication does not produce exhaust gasses. With care, much lubrication can be recycled. Ask your dealer how this is done when servicing. Battery packs probably will use coolants in the foreseeable future, e.g. anti-freeze around the individual battery cells to get rid of the heat. These coolants can also be recycled.] Use and recovery of dichloromethane (DCM) in battery production can also be pitched, since Tesla has a patent on their process. Again, ask your dealer if you are interested.
  10. A BEV should have a long list of high tech features: autopilot (Tesla has driven 1M miles on autopilot) for autonomous driving, lane departure warning, auto park, radar driven auto braking, multi-zone HVAC, 15-20 speaker hifi, seat heaters, remote controls from a mobile app, GPS navigation, event data recorder (EDR) and automatic collision notification (ACN), digital keys, telematics, anti-theft, dash-cams, … Bundle as many as possible into base price of car. This list will vary (and improve) each year.

In summary, a BEV manufacturer needs to have models that compete with comparable Tesla models. At a particular price range, many points of competition are subjective, e.g., beauty, service, high tech features, safety, retail stores, near-by charging stations, environment, warranties and total cost of ownership, etc. Points of objective competition need to be close, e.g., range, acceleration, handling, braking distance, etc. I wonder if the strategy of high-end, expensive models for Tesla competitors is going to last much longer. Volume and manufacturing efficiency will be necessary to drive costs down for price comparisons, and the large classic automobile manufacturers may have an advantage here. For battery costs, partnering with a large battery manufacturer, as Tesla has done with Panasonic, seems like a good idea no matter the chosen battery cell form factor. The Chinese battery maker Contemporary Amperex Technology (CATL) and the Korean LG Chem are contracting with some major EV companies. There are of course many other battery manufacturers. Ford’s $22 Billion investment in EV’s, mentioned above, is probably what it will take to compete with Tesla.

BEV Manufacturing

Who makes battery-only electric vehicles? Here is my cut on a current list. Wikipedia has a somewhat outdated list (also here) from which I learned about several foreign BEVs. Many BEVs are tiny urban-only cars (micro cars) with less than 100 mi range. While interesting, they are not competing with Tesla – at least not yet. Some classic car companies are still only selling plug-in hybrid (PHEV) cars. I’ve listed them below without any detail just to indicate that the company has no BEV products (that I know of); many have announced BEV intentions. Tesla has more models than anyone now in the US, and I can’t find a BEV that competes with and is better than a particular Tesla. Range, i.e. batteries, is still the major point of competition. Henrik Fisker, the famous automobile designer now heading Fisker Automotive, states that to compete with Tesla, a BEV must move to a different level of competitive technology.

  • Aston Martin: plan to electrify the DBX crossover.
  • Audi: A3 Sportback e-tron PHEV
  • Daimler: Has plans for ten BEVs by 2022 including Mercedes listed below.
  • BMW: i3, BEV (others are PHEV)
  • BMW Brilliance: Zinoro 1E, BEV, 93 mi range, China only
  • Bolloré: Bluecar BEV, 93-160mi range (highway-urban), France (EU) only
  • BYD (Build Your Dreams): Tang, Song, Qin PHEVs; Song, Qin, e5, and e6 BEVs; Tang EV500 SUV BEV 310mi range, Tang Song MAX DM PHEV; T3 BEV mini-van; no US imports yet and no US prices.
  • Chery: QQ3 EV, 62 mi range, state owned China only; multiple QQ models
  • Chevrolet: Bolt BEV (Volt is PHEV), 238mi range, $37.5K
  • Chrysler: Pacifica PHEV
  • Citroën: C-Zero = Mitsubishi i-MiEV
  • Courb (Cogitare Urbem): C-Zen, 81-72 mi range. Bankrupt?
  • Daimler: Smart ED, (“ED” = electric drive), BEV
  • Dyson (the UK vacuum cleaner company): BEV under development for 2020.
  • ElectraMeccanica: Solo BEV, 100 mi range, Canada only, Chinese investment
  • Fiat: no public plans other than to spend $9 billion on “cars with electric motors”. Has the very small 500e for California and Oregon only, 84 mi range, $33.9.
  • Fisker: 2021 EMotion BEV, 400 mi range, $129.9k; 2021 SUV 300 mi range, $40k+.
  • Ford: Focus Electric BEV, 115mi range, $30k, others PHEV. Plans 16 EV models by 2025.
  • Girfalco: Azkarra BEV, 3 wheeled performance vehicle in development in Canada
  • Groupe PSA (Peugeot, Citroen, DS, Opel, and Vauxhall): plans 15 “electrified” new cars starting in 2019.
  • Honda: Urban EV 2019; plan for compact EV (BEV?) by 2020 in Japan and longer vision for 2030; 15,000+interest registrations for the e Prototype (for family of BEVs), 125 mi range.
  • Hyundai: IONIQ Electric BEV, 105mi range, $30.3k
  • Indica: Vista EV, 120 mi range. Indica (Tata) is a large company and sells this EV globally in test quantities.
  • JAC: J3 EV, BEV, 81 mi range, no models for US yet. Chinese state owned.
  • Jaguar: I-Pace SUV BEV.
  • Kandi Technologies: KD5011 BEV (+ 9 other models), China only
  • Karma: Rivero PHEV, future Pininfarina partnered Vision (part of “New Dawn” initiative) BEV announced in Shanghai show.
  • Kewet: Buddy BEV, 50 mi range, popular Norwegian car since 2010.
  • Kia: Soul EV, BEV, 92mi range, $33.1k; Telluride PHEV SUV; 2019 eNiro BEV 238mi range, $39k+
  • Lada: Ellada, Russian BEV, possibly bankrupt. 93 mi range.
  • Lightening: Lightening GT, BEV sports car, 149 mi range, London based
  • Mahindra: e2o plus, BEV, 75 mi range, sold and not popular in UK. Mahindra is a huge Indian conglomerate.
  • Mercedes: GLE 550e, PHEV; SLS AMG (BEV variant), 160 mi range, limited edition?
  • Mitsubishi: i-MiEV BEV (discontinued)
  • MW Motors: 4 motor Luka EV, 186mi range, Czech, no US
  • Nissan: LEAF BEV, 106mi range, $28.5k; Leaf e+ has 239mi range, $48.7k
  • Opel: Ampera-e, 5 door subcompact hatchback BEV, 320 mi range, EU only?
  • Piëch: Mark Zero, 311 mi range, fast charging 3 motor very fast sports-car. Other models: 4 seater, and sporty SUV, start production 2020.
  • Pininfarina: Battista, Rimac 4 wheel drive $2.6M performance sports car. 150 will be sold in US. Has 120 kWh battery, 280 mi range.
  • Porsche: Cayenne S E-Hybrid PHEV; 2019 Taycan BEV
  • Renault: Zoe (Europe’s top EV)
  • Rivian: (late) 2020 Pickup Truck and SUV, 230+ to 400+ mi range (depending on battery pack), $69K+
  • Tesla: Models S, X, Y, 3, 200+mi to 300+mi range, $50-100k. (Discontinued Roadster will reappear 2020); 2020 Semi 500+ mi range; 2020+ Pickup ???
  • Toyota: Scion iQ BEV (too small); Prius PHEV; future BEVs will go first to China.
  • Volkswagen: e-Golf BEV, 124mi range, $29.8k; plan 50 BEV models by 2025 (zero hybrids).
  • Volvo: XC90 T8 Twin Engine PHEV, Polestar 2 BEV



Lithium Ion Batteries


Li-ion Batteries

Batteries have evolved and improved by about 7-8% every year, with the cost coming down at the same rate. They now have three applications that drive progress: Electric cars, power storage for solar and wind when one or both aren’t making much electricity, and for caching power, e.g. storing when power is cheap, and discharging when it is expensive. Batteries have evolved past automobile lead-acid starting batteries and powering toys, to giant commercial applications. See my old post “Metal-Air Batteries” as well as the post “Storing Energy from Solar Arrays” to see where my brain was several years ago.

Rechargeable Batteries and Nickel-Cadmium

Aside from lead-acid starter batteries in my cars, my early portable devices with rechargeable batteries all had 1.2v Nickel-Cadmium, NiCd, cells. These had a “memory” problem and needed to be regularly fully discharged and then fully charged. Partial discharges and partial recharges got “remembered” by the battery, and it became self-limiting. Materials for the NiCd batteries were expensive, and the cadmium in particular was toxic and was bad for land fills. NiCd batteries also had a high self discharge and needed recharging after storage.

There were many nice features of NiCd batteries. They had a high discharge/recharge cycle count. They could be recharged quickly with little stress. They had good load performance and good cold weather performance. They became available in a wide variety of cell sizes. In the 1980s, an “ultra-high capacity” NiCd battery was introduced, but it had a reduced cycle count due to higher internal resistance.

Nickel-metal-hydride batteries

Starting in 1967, research in nickel-hydride (NiH) and later in nickel-metal-hydride (NiMH) solved early problems with rapid self-discharge and internal corrosion, but specific energy remained a problem with NiMH batteries. Today NiMH is the most available rechargeable battery for consumer use, and most battery manufacturers such as Duracell, Energizer, Panasonic, Rayovac, and Sanyo provide all popular sizes such as AA, AAA, etc. NiMH batteries have essentially replaced NiCd batteries for consumer use.

Lithium-ion batteries

Lithium is the lightest of all metals, and, in a rechargeable battery cathode, can have the largest specific energy per weight. Unfortunately, cycling produces dendrites on the anode whose growth will penetrate the separator causing a short. The cell temperature then rises quickly and approaches the melting point of lithium; this causes thermal runaway and fire. The inherent instability of lithium thus shifted focus to various lithium ions for the cathode. Research continues on how to avoid or mitigate lithium dendrites. In 1991, Sony brought out the first commercial Li-ion battery. Li-ion cathode batteries have a lower specific energy than pure lithium anodes, but are much safer with proper voltage and current limitations. There are many Li-ion structures and hence many types of Li-ion batteries, each with different properties. The high cell voltage of 3.6 volts provides a Li-ion battery high specific energy. It has good load characteristics and a flat discharge curve over a voltage range of 3.7 to 2.8 volts.

In 1994 the cost of a Li-ion 18650 cell (the last zero indicates cylindrical, 18mm diameter, 65mm high) was over $10 and the capacity was 1100mAh., but by 2001 the cost had dropped below $3 and the capacity increased to 1900mAh. Today the 85 kWh battery pack for Tesla’s Model S contains 7,104 Li-ion 18650 cells. Estimating $130 per kWh, the cost per 18650 cell is about $1.56. Each cell has a capacity of 85000/7104 = 11.97 Watt-hours at 3.6 volts = 3324 mAh. Costs are projected to fall below $100 per kWh in the next few years.

Form Factors

People are familiar with A, AA, and AAA battery form factors as well as many others that can be found in any retail store that sells batteries. Tesla started using the 18650 form factor mentioned above, but for the Model 3 and beyond, Tesla is using the 21700 form factor for its Li-ion batteries. (Again the last zero indicates cylindrical, with 21mm diameter and 70mm height.) This is a 25% increase in volume. It also tends to reduce the number of contacts and cells within the battery pack making the battery pack a bit easier to manufacture. The energy density has improved 20% according to Tesla, and the cobalt content has been reduced while increasing the nickel content reducing cost. Unfortunately, the core temperature is 20% higher, reducing the life cycles 20%. This degradation is acceptable, but larger form factors may have safety problems.

Of course, a form factor can have almost any Li-ion chemistry, In fact, different applications can use different chemistries. For example, the Tesla Model 3 uses Li-NiCoAlO2 (NCA) while the commercial Tesla PowerPack in Hornsdale, Australia uses Li-NixMnyCozO2. (NMC). Both use the 21700 form factor.

Li-ion Battery Cathode Chemistries. Note industry trend is to use Mn to reduce the use (and cost) of Co.

Name Cathode Formula Abbr Use Comment Manufacturer
Lithium Cobalt (Cobaltate) Li-CoO2 LCO Cellphones, laptops, cameras First Li-ion battery. Heats up at high voltage. Doped for increased energy density levels, but lower life-span. Cobalt is rare & expensive. Sony 1991, Chinese
Lithium Manganese (Di-)Oxide Li-Mn2O4 LMO Power tools, small portable devices Nissan Leaf, Chevy Volt, BMW i3 UltraLife, Varta, SAFT, Regulus, Fanso, Zeus,
Lithium Iron Phosphate Li-FePO4 LFP Power tools, small portable devices Safe but low volumetric energy. 32650 size. BYD, OptimumNano Energy.
Lithium Nickel Manganese Cobalt Oxide Li-NixMnyCozO2 NMC EVs, (Tesla) grid storage, Hornsdale Good cycles at high capacity, but lower than NCA. Material patented and licensed. Used Samsung for Hornsdale
Lithium Nickel Cobalt Aluminum Oxide Li-NiCoAlO2 NCA (All Tesla) EVs, grid storage Higher cycle stability at high capacity. Al is used instead of Mn to stabilize crystal structure. Low material cost. Enters thermal run-away at lower temperatures than NMC. Thus, limited to lower capacity cells. Material patented and licensed. Tesla has “gigafactory” in LV.
Lithium Titanate Li4Ti5O12 LTO EVs, grid storage, anode Rechargeables can take 3-7000 cycles. Compared to 1000 or so for NCA. Works well for busses. Altairnano, Lelanche, Microvast, Toshiba, Seiko, Yabo

Li-ion Anode. Always some form of graphite, but trend is to go towards Silicon, which can store 10x more energy than graphite per volume and 3x the energy per mass. However, Silicon expands 400% during charging. Allowing for this expansion would take up too much volume; on the other hand, just doping the anode with a little silicon oxide, SiOx, appears to be a good compromise. The original Tesla Model S, did not do this, but later the Model S and the early Model 3 used 5-15% SiOx. Future Tesla 2170 battery cells may go as high as 35-75% with the actual formula a closely guarded Tesla trade secret. Sadly, any silicon on the anode reduces the speed at which the battery cell charges.

Recycling Lithium Ion Batteries

While lithium is relatively abundant, its cost is high and cost effective recycling Li-ion batteries method to recover the lithium, cadmium, nickel, and iron in them needs to be developed. Umicore Recycling Solutions in Belgium does this under EU laws. For the US, if we want to keep these metals out of our land fills and our water supplies, then we need to require every battery cell to have a “deposit”, say of $0.10 each. The 7,000+ battery cells in a Tesla then would be worth $700+ to a recycler.

Solid-state Batteries

When I first heard this term, my mind boggled and thought of a battery made out of circuit boards! Actually the word “solid” refers to substituting the liquid electrolyte in the Li-ion cell with a solid. Wikipedia calls this a “Glass Battery”. It was invented by John Goodenough and colleagues John is credited with inventing the original Li-ion battery, and the story goes that his colleagues then took his ideas to Japan before patents were filed. John and Maria Braga published their solid-state battery ideas in Energy and Environmental Science in December 2016. Both the anode and cathode are coated with lithium; however, the lithium plated on the cathode current collector is thin enough (on the order of a micron) so that the Fermi energy is lowered to below the level of the Fermi energy on the lithium anode. The electrolyte is a highly conductive glass formed from lithium hydroxide and lithium chloride and doped with barium. The claims are double the energy density of a lithium-ion battery, with more than double the number of charge/discharge cycles possible. It is further claimed this battery has a much shorter charging time (minutes rather than hours). It is also safer as dendrites do not form and no flammable liquid is present. Lithium may be swapped with sodium (Na) at a loss of 0.3v per cell.

Optimizing CPV Systems


Optimizing CPV Systems

Concentrating Photo-Voltaic (CPV) systems have some competitive advantages, for example,

  • CPV uses land efficiently, i.e., MW/acre is excellent for CPV
  • CPV does well when ambient temperatures are very high, e.g. in excess of 110 degrees Fahrenheit (43°C).
  • CPV needs no water to operate and very minimal water for maintenance work.
  • CPV seems to have very minimal ecological impact – better than wind and other forms of solar power generation.

Thus CPV works well in deserts where there is a nearby connection to the grid, and where the regional electric company can take all the power that a CPV farm generates and can put up with no power at night and slightly irregular power due to occasional clouds.  (Today CPV systems tend not to have energy storage mechanisms to smooth out the energy delivery to the grid.) This defines the CPV “niche.”

CPV systems have the disadvantage in that they are complex.  Starting with three layer multi-junction photovoltaic cells, which are expensive in their own right and somewhat complicated to wire into arrays and panels, they need a Fresnel lens to concentrate sunlight onto (or more precisely into) these cells.  They require that the sunlight rays be orthogonal to the plane of the panel, and this means that the panel must track the sun using a two axis system that adjusts both the azimuth and polar angles of the panel.  Large panels need to be mounted relatively high so that the panel clears ground objects as it “tracks” during the day.  A robust structure is needed to support the system weight and the  forces of wind on the system.  Depending on the locality, service roads and fencing might have to be installed.  Finally each CPV structure needs an inverter to convert DC to AC, and a connection to the grid.  The cost of each of these components is, of course, the first point of attack in optimizing CPV systems.  These are the capital costs that need to be optimized.

There are of course non-trivial, non-capital installation, calibration, maintenance, and operational costs.

The capital, installation, and operational costs of a CPV system can be mitigated in the near future by a favorable regional government-dictated Feed-in Tariff (FiT), which guarantees a grid connection, a long term contract, and rates that take into account these costs and that guarantee an operational profit. Italy’s FiT is particularly advantageous, since it has a special tariff table for CPV. [1]  Now if competition weren’t enough motivation for CPV vendors to drive costs down, most Feed-in Tariffs reduce the guaranteed rates by a small percentage each year to motivate the vendors to take advantage of technology improvements and reductions in operating costs.

As mentioned in an earlier post on Levelized Cost of Energy (= a system’s lifetime future costs divided by the lifetime energy it will produce) there are many components to lifetime costs, each of which needs to be consciously and systematically driven down by the CPV vendor. What is needed here is a company-specific model for these costs and a continuous improvement program to drive each cost component down.  NREL’s System Advisor Model (SAM) is a very nice start (and its earlier versions motivated the definition of LCOE), but a company needs more detail to optimize costs.

For example, a CPV system is particularly sensitive to being aligned precisely (to a small fraction of a degree) to the sun.  This necessitates high precision in its two axis tracking system.  In addition to its additional capital cost, a tracker has additional installation and maintenance costs.  Mounting a tracker on a high pedestal created additional weight and hence wind force factors.  Each of these details (accuracy, capital cost, installation cost, maintenance cost, weight, and required structural support to address wind forces) must be optimized by the CPV vendor.

LCOE isn’t the only useful metric for a CPV vendor to consider.  Now marketing folks and the press like big numbers, and hence the peak power or Watts-Peak (Wp) makes a lot of headlines. It is the maximum power that can be generated by the system.  Sometimes this number is tempered (no pun intended) by NREL’s Standard Test Conditions (STC) to get a “name plate” rating.  Probably a little more interesting is the Energy to Peak Power ratio.  Define:

SI = Site Irradiation (kWh/m2/yr)

RI = Rating Irradiance (kWp/m2)

PCE = DC to AC power conversion efficiency

ATE = Average temperature efficiency

EPP = Energy to Peak Power Ratio = SI*PCE*ATE/RI

The Site Irradiation, SI, is really the actual energy produced by the CPV system per unit area, say over a year.  Since the energy produced varies with time, this needs to be a sum over time-intervals small enough so that the energy produced in each time-interval is approximately constant.  Similarly the ATE varies with time, since the device will heat up during the day causing increased degradation.  One then uses time-intervals small enough so that the temperature during the time-interval is approximately constant.  PCE is just the inverter efficiency.  The EPP ratio is a little flawed in that the numerator has the factor of hours per year in it.  A mathematician would divide it out, but the industry tends to leave it in.  Oh well, …

While LCOE has most of the EPP terms in its ultimate calculation, it is none-the-less instructive to track this ratio as well as to optimize each term.  Note that the Energy to Peak Power ratio is a function of locality as is LCOE.

The significant improvement in solar cell efficiencies has driven CPV’s LCOE down in past years due primarily to increased energy production.  PV, on the other hand, has had its capital costs driven down dramatically by massive Chinese government investments.  This has driven down fixed thin film PV’s LCOE.  The net result of these two trends is to make thin film PV more attractive EXCEPT in the niche described earlier for CPV dominance.  This race of technology and manufacturing improvements will, of course, continue.  Unfortunately, the three major CPV vendors, Amonix, Concentrix, and SolFocus are all going after smaller numbers of large “utility sized” sites.  This doesn’t lend itself to cost or manufacturing efficiencies as compared to the goal of putting thin film PV on every rooftop in the world. CPV vendors will need to invest to compensate for this.  It will be a challenge.



[2] “LCOE For Concentrating Photovoltaics (CPV)” by Warren Nishikawa, Steve Horne, Jane Melia,, SolFocus Inc., 510 Logue Ave., Mountain View, CA 94043 International Conference on Solar Concentrators for the Generation of Electricity (ICSC – 5), November 1619, 2008, Palm Desert, CA USA ( )

Levelized Cost of Energy (LCOE)


Levelized Cost of Energy

For any power generating system, one can compute the “levelized cost of energy” (LCOE) over the predicted lifetime of the system.  It is the ratio of the present value of the total cost of operation or ownership (TCO) to the total energy generated (TEG) over the predicted lifetime of the system.  This ratio, LCOE =TCO/TEG, looks simple, but the devil is in the details (as my mother used to say.)

LCOE does have a simple interpretation.  First note the units:  Today’s cents, dollars, Euro’s, etc. are in the numerator, and kilo-watt-hours (or mega-watt-hours) are in the denominator.  Usually it is cents per kWh or dollars per MWh.  If you want to build a power plant, you definitely want to sell the power you put onto the grid at a price greater than your LCOE, or you will lose money.

You can also compare the cost efficiency of various systems, and indeed, of various types of systems.  Here’s a table of such from a respected government source [1]. It indicates how LCOE can vary by region.  E.g. Transportation charges for coal, amount of sunlight and incidence angles for solar, amount of wind for windmills all vary by region.  However interesting these tables are, there is no guarantee that the LCOE was calculated fairly in each case.  Thus before making any decisions based on LCOE numbers, be sure you really understand how they are computed.  The text after the table is a start.

Regional Variation in Levelized Cost of New Generation Resources, 2016.

Plant Type Total System Levelized  Costs
(2009 $/MWh)




Conventional Coal




Advanced Coal




Advanced Coal withCCS




Natural Gas-fired
Conventional Combined Cycle




Advanced Combined Cycle




Advanced CC with CCS




Conventional Combustion Turbine




Advanced Combustion Turbine




Advanced Nuclear








Wind – Offshore




Solar PV1




Solar Thermal
















Energy Information Administration, Annual Energy Outlook 2011,
December 2010, DOE/EIA-0383(2010)

For example, this table indicates that wind is comparable to natural gas.  This surprises me.  Also note how much more offshore wind costs.  This is particularly surprising given the large investment that is under weigh along the east coast of the U.S.  Hydro is a winner, but as my son Sam pointed out to me, it is unlikely that these numbers compute the damage done to the fishing industry (esp. salmon fishing) by these dams (environmental damage can be modeled as uninsured costs, see below).  This is another devilish detail.

Now, let’s look at the devilish details:

First the predicted or expected lifetime of the system assumes excellent maintenance and reasonable upgrades.  At the beginning of the lifetime, there is the original (capital) cost of construction and of the hook-up to the grid, and at the end of the lifetime there is the decommissioning and waste management of all the remaining materials.  The original cost needs to include things like access road improvements, right of way purchases, the installation’s fair share of grid improvements necessary for the hookup, etc.  Some towns, knowing that all the construction vehicles passing over its roads will wear on those roads, may want compensation in order to repair or refurbish them after the construction.  This should be included in the original cost.  Here the cost of financing needs to be carefully included.  The decommissioning cost is often (fraudulently in my opinion) excluded.  It must include tear down costs, land fill costs for the debris, and the safe storage of chemicals, fuels, and radioactive material.  It might include, instead, the cost of a complete refurbishing of the system to make a totally new power generation plant.  In this case, one must fairly separate the decommissioning and waste management cost of the old system from the original cost of the new system.  The residual value of the old system needs to be subtracted from its TCO.  Similarly, if waste steel is recycled, its residual value needs to be subtracted from the old system’s TCO.

Note:  Some people believe that if nuclear power plant LCOE included the total decommissioning and cost of nuclear waste removal and storage, then nuclear simply wouldn’t look very attractive economically.  As a boy, I used to think that waste nuclear fuel should be put into rockets and shot into the sun.  Sadly, this quite reasonable idea is not feasible economically.

Now during the lifetime of the system, there is a lot of operational cost, maintenance, repairs, and upgrades.  There are many of these.  Here are some:

  • Land lease costs.
  • Labor, travel, fuel, materials, etc. costs for operations and maintenance.  Note that some fuel prices, e.g. nuclear and petroleum, might have difficult-to-predict cost variations due to political considerations.
  • Large, infrequent upgrades or replacements.  A ten year replacement for inverters is often mentioned.
  • Insurance costs.
  • Property tax costs (but not income tax as that speaks to profitability not cost).
  • Utility costs, e.g. water, sewage, network communications, telephone charges.
  • Uninsured liability, theft, vandalism, disaster, and ecological damage costs.
  • Future green-house gas GHG charges.

These all have to be estimated over time and space (region), the present value of these costs needs to be calculated, and added up, we get the total cost of ownership, TCO.  As mentioned above, these costs will vary by region and of course over time. Some costs are correlated to an appropriate conflation index, and others need to be modeled.  All assumptions need to be carefully documented.

Finally, the economic assumptions for the present value calculation of all these costs must be documented.

Let’s turn to the denominator, the total energy generated over the predicted lifetime of the system.  For very stable sources of energy, e.g. nuclear, hydro, coal, natural gas, etc., one can reasonably assume a policy of steady consistent energy production, e.g. a certain number of kWh per day.  For wind, solar, geothermal, tidal, etc, there are simple models for energy generated, say per year, and there are more detailed models that would depend on weather and warming trends.  These latter can be quite sophisticated.  There are some additional subtleties to consider.  For example, not all of the power rating of the system gets onto the grid as energy, i.e. as electricity.  Some of this difference is standard due to energy conversions and efficiency of equipment.  For wind and solar farms, not all of the equipment is 100% operational; for example, some of it may be down for routine maintenance or repairs.  (PV systems need to be cleaned regularly, and the system will degrade as its solar cells or lenses slowly get dirty.)  Some reasons are more subtle, e.g. time shifting energy production via the use of an energy storage mechanism (CAES, liquid salt, MgH2, batteries, etc.)  Conversion both to and from the storage mechanism produces an energy loss.  Thus the algorithm for time shifting needs to be considered in the calculation for LCOE.

Given that some of the variable components of both TCO and TEG are “random”, i.e., depend on random events such as weather and politics over time, it is often appropriate (and easier) to make assumptions on these random event distributions and run Monte Carlo simulations for the calculations.  Argonne Laboratories has written a paper on this.

Note that the calculation of LCOE avoids (except for the reasons for time shifting) what the electric companies will pay for energy put onto the grid.  LCOE is one massive average over a long (20-30 year) lifetime.  Electrical rates are quite another thing.

Electrical rates vary across the day, with utilities charging commercial enterprises more for electricity during “peak hours” than during “off hours”.  The differences can be considerable.  Solar systems generate most of their power during peak hours.  If a solar system is directly substituting for utility company power during peak hours, then the value to the owner of that system will be, during these hours at least, equal to the peak rate the electric company charges. This type of logic is not directly factored into LCOE calculations; however, a favorable power provider agreement (PPA) between the generator owner and the utility can improve the deal for financing charges.  Residential and most commercial installations of solar power will not get a favorable agreement with the utility company.  Per the California Public Utility Commission, excess electricity generated and not used, i.e. put back onto the grid, is to be compensated annually at the average spot rate for the year – better than nothing, but far less than peak rates and not a real incentive to install solar power on your roof for the purpose of making money by selling the excess energy.

As explained before in these notes (here) irregular sources of utility scale energy such as wind and solar may well be more profitable with local energy storage.  This would allow a base level of energy to be put onto the grid, and also some additional energy for peak times.  To model this, a revenue model needs to be created in parallel with the LCOE model.  This can be done in a spreadsheet, but it can also be done with Monte Carlo methods.  These models need to be part of the pro forma economic analysis done at site selection and system design time.  The PPA negotiation with the utility company needs to conform with the model results.

Finally, NREL publishes a simple LCOE calculator here, which can be used to test any LCOE calculation for reasonableness.


[1] Levelized Cost of New Generation Resources in the Annual Energy Outlook 2011

Smart Appliances and Energy


Smart Appliances and Energy

With more and more household appliances using microprocessors to add “smart” features, their energy consumption can become an issue.  In fact, even the dormant state of these appliances can consume significant amounts of electricity.

One of the worst offenders is the now ubiquitous cable TV box, of which my house has half a dozen.  These use power to retain state.  This is superficially reasonable, since the catalog of the next several days of TV shows is part of that state (as is all the personal settings.)  Downloading this catalog takes several minutes, which would be annoying for most consumers, who want “instant” access to their TV show listings.  As these boxes contain Internet connections, which take time to establish a connection, there will be a tendency to use power to maintain that connection 24 hours per day.  Here some design work is required to minimize energy consumption while maintaining fast reaction times when the TV is turned on.

Now we move to refrigerators.  One can imagine quite a number of applications for a microprocessor in the refrigerator.  Recipes from the Internet that pop up when a food bar code is scanned, or entered into the computer, but probably a more useful feature would be an inventory of what is being stored (fresh or frozen).  While storing an item, swipe its bar code so that the system knows when you first stored it and hence how old it is later.  Enter its expiration date and location in the refrigerator.  Coming back to recipes, how about a list of recipes that can be made from ingredients in the refrigerator?  Nice!  Even nicer would be to access this inventory via cell phone when at the market.  “Do I have any fresh cilantro at home?”  My current refrigerator simply beeps at me with the door is left open, but why not send my cell phone a message?  Of course, access to the Internet allows access to video based cooking instructions to be downloaded and played.  Want to see that technique to whip up a great soufflé?

Smart stoves and ovens have a different play when hooked up to the Internet.  My favorite would be to warm up my oven as I’m heading home from the market.  Integrated temperature probes are popular with microwaves, but should be integrated into ovens as well.  Sensors that turn off that stove when the pot has boiled away all liquid would be a nice safety feature.  OK, all these features are nice, but what is the cost of the energy?  Again, some design work is needed to minimize energy consumption and still to maintain fast power ups.

Refrigerators have another option that was discussed briefly in an earlier post.  When it is cheaper to use electricity at night, a refrigerator can wait until night time to make the system extra cold so that it can more easily ride out usage during the day.  Note that if the building has solar power to augment the utility provided electricity, the solar power is “free” during the day and expensive at night.  Thus, it makes sense to keep the system extra cold during the day and to almost power off at night.

My current microwave’s defrost features are terrible.  Look, I want to defrost a steak quickly without partially cooking it.  I also don’t want to wait an hour defrosting a big chicken.  The smarts to do this are SMOP (“simply a matter of programming”).  My microwave gives me a ridiculous choice for defrosting options.  How about getting the right option off the Internet by scanning its bar code?  Also, a microwave should probably be hooked up to a digital scale to weigh things, but putting the scale into the microwave itself has its charm.  A lot of these features can be implemented without using too much excess energy.  In fact, considerable energy can be saved, simply by not overcooking things!

Now, who is going to invent the “green” robot that does all my cooking for me?

Of course the moral here is that smart appliances are coming, and I hope that industry will embrace saving energy.


Storing Energy as MgH2


Storing Energy as MgH2

With wind and solar power generation, it is often desirable to store energy locally rather than to put it onto the grid.  For example,

  • Sometimes the rates paid by the electric company are not favorable, e.g., at non-peak times, or are even negative.
  • Usually the electric company wants a “base load” to be provided, i.e., a minimum amount of electricity that goes onto the grid 7×24.  Neither wind nor solar can do this without burning another fuel such as natural gas or hydrogen.
  • A capital cost reduction can be partially realized if the generation system is designed NOT to generate more than a certain maximum level of electricity, with the rest being stored to address the base load issue.  The reason for “partially” is that the capital cost of the storage system needs to be factored into the total cost.

One storage possibility is to store the energy as hydrogen gas using electrolysis to break down water into hydrogen and oxygen:

2H2O + energy –> 2H2 + O2

With an 80% efficient electrolysis unit, it takes about 50 kWh of electricity to create 1 kg of hydrogen. The hydrogen could then be used in a fuel cell or converted gas engine to generate electricity.  This is great except for the “detail” of storing the hydrogen.  (What to do with the resultant oxygen is another detail.  It can be bottled and sold, or simply released into the air.)  Most people suggest compressing the hydrogen possibly to a liquid form, but that takes considerable energy, and the result is not economical for the production of electricity.  Not compressing it takes too much storage and pumping to move it around.

Multiple methods for storing the generated hydrogen as hydrides, e.g., magnesium hydride, MgH2, have been developed over the years.  For MgH2, they involve grinding the magnesium in a hydrogen environment at pressure (15 Bars or so), at high temperature (in excess of 300°C), and in the presence of a catalyst. (Various catalysts have been proposed, including MgH2 itself.) This process gives an initial supply of MgH2 for use in an energy storage cycle.

The folks at Safe Hydrogen mix the resulting MgH2 into a “slurry” by adding light mineral oil and some dispersants. The dispersants aid in keeping the MgH2 particles from agglomerating and help to stabilize the slurry. The mineral oil helps to protect the MgH2 particles from inadvertent contact with moisture in the air and provides the liquid medium for the slurry.  The resulting slurry is then cooled to room temperature for stable storage.  This process is described in their patent US 2010/0252423 A1. The slurry looks a lot like thick paint.  Here’s a photo from one of the Safe Hydrogen papers, links to which can be found on their web site.70 Percent MgH2 Slurry

At ambient temperatures, the slurry is stable, not highly flammable, and can be pumped, transported, and stored in standard tanks and trucks.  It has stored energy by kg or by liter (L) as high as [0] 3.9 kWh/kg and 4.8 kWh/L.  Compare this to gasoline which has 1.8 KWh/kg of practical energy storage within 12.8 kWh/kg of total theoretical energy storage. [1]

The slurry can be converted back to hydrogen and recycled as follows:


The first technique is to add water to release the hydrogen:

MgH2 + 2H2O –> Mg(OH)2 + 2H2

The resulting byproduct, magnesium hydroxide, Mg(OH)2, is, in its pure form, a white power, and when mixed with water forms a suspension that is essentially the same as “Milk of Magnesia.”  Recycling the Mg(OH)involves several steps:

  1. The separation of the oils from the byproduct slurry for reuse.
  2. The calcination of Mg(OH)2 to MgO by heating to around 300°C,

Mg(OH)2 –> MgO + H2O,

  1. The electrolytic reduction of the resulting magnesium oxide using the “solid-oxide • oxygen-ion-conducting membrane (SOM) process developed atBostonUniversity[2].

2MgO –> 2Mg + O2

  1. The hydriding of the Mg obtained in the preceding step and H2 (obtained by additional electrolysis of water) to MgH2, is done by mixing magnesium powder with magnesium hydride powder and hydrogen at about 300°C and 10 Bar.
  2. The production of new slurry from the MgH2 and the recovered oils.

In this process, slurry is pumped into a stream of hot water to mix the slurry with the water. The mixed stream then flows into a reaction chamber where the bulk of the reaction takes place, releasing hydrogen. Several injections take place in quick succession to take advantage of the heat from the previous reaction. The byproducts of this reaction collect in the bottom of the reactor. Periodically, the reaction chamber is flushed by filling it with water to recover the oils from the slurry. The water level is reset and the injections resume. Also periodically, the byproducts are moved from the bottom of the reactor to the byproduct separation chamber. In the byproduct separation chamber, the water is filtered from the solid byproducts and returned to the water storage container. One can readily hydride magnesium by mixing magnesium powder with magnesium hydride powder and hydrogen at about 300°C and 10 Bar [This step is described in detail in the above cited patent.].  The heat produced by the electrolysis process was estimated to be enough to satisfy the heating requirements of the system in continuous operation.

Effort needs to be performed to condense magnesium into a powder from the vapor produced by the SOM process. To minimize the fire hazards associated with magnesium powder, the powder should be immediately hydrided, and the resulting magnesium hydride should proceed directly into a slurry production process.

According to Andrew McClaine, CTO at Safe Hydrogen, “We are currently scaling up from a laboratory scale of 2 kWth to a scale of 20-40 kWth.”  In other words, this technology needs a lot of development before it can scale to utility sized operations, which would require tens to hundreds of MWh of energy stored.  Note that 10MWh would take about 2,000 liters of MgH2 slurry.  Safe Hydrogen’s estimates on cost seem reasonable, but the process is complex with lots of variables.  It usually takes a decade for such technology to become cost effective and mass produced.

McClaine also points out that there is another technique to release hydrogen from the slurry.  It is to heat it to around 280°C.  This releases some of the hydrogen rather efficiently and allows the slurry to be replenished later by adding hydrogen from the electrolysis process.  Apparently this process can be repeated efficiently approximately 100 or so times, before the complete first process needs to be performed.  Safe Hydrogen is working on optimizing this combined technique and on increasing the number of cycles from 100 to potentially 1000 or so.

Refining all these techniques may well produce a commercially viable product, even at a scale of 20-40 kWth.  Safe Hydrogen seems to think so.  It appears that smoothing out the energy produced from wind farms may have an earlier commercial product than transporting the slurry and producing hydrogen elsewhere. [3]


[0] Certain proposed lower cost processes will produce a lower energy density of the slurry.  Safe Hydrogen is experimenting with various processes.  Personal communication Andrew McClaine, 8/28/2011.

[1] Journal of Physical Chemistry and Letters

[2] Solid-Oxide Oxygen-Ion-Conducting Membrane (SOM) Technology For Production Of Magnesium Metal By Direct Reduction Of Magnesium Oxide, D. E. Woolley and U. Pal, Department of Manufacturing Engineering, Boston University, Boston, MA 02215, G. B. Kenney. ElMEx, LLC, Medfield. MA 02052

[3]  Storing Wind Energy as Hydrogen, David Anthony and Ken Brown, reprinted in Green Economy Post, August 15, 2011.

Metal-air Batteries


Metal-air Batteries

As discussed in a previous post, wind and solar generators need energy storage mechanisms for a variety of reasons.  This post discusses some promising new battery technology, rechargeable metal-air batteries.  Single use metal-air batteries have been around for years.  The new technology here is to design them so that they are efficiently rechargeable.

There are three sizes of applications to think about:  little button batteries for electrical gadgets (usually single use), batteries for electric vehicles, and batteries to smooth the energy generation of utility-sized wind and solar generators.

The current commercial state-of-the-art, Li-ion batteries, which are used in today’s electric and hybrid vehicles, are really heavy and they cost a lot!  They have some other problems.  First the range today of an EV is 50-200 miles whereas we’re used to say 350 miles.  Second, the charging time is in the order of 7 hours, whereas we’re used to 3-4 minutes to refill a car’s gas tank.  These problems, of course, get worse when scaled to utility sized units; hence, the industry is driven to a new generation of battery.

Metal-air batteries use oxygen directly from the air, which allows for higher total energy density due to unlimited cathode capacity.  This definitely will reduce the weight.  The possible metals investigated by the industry are Zn, Fe,Al, Mg, and Li, with zinc (Zn) and lithium (Li) being the most frequently discussed.  One model predicts that the overall theoretical energy density of polymer electrolyte Li-air battery could be as high as 2790 Wh/kg and 2800 Wh/L, which is comparable to gasoline-air combustion engines [1].  The following table comes from Chemical and Energy News, 11/22/10.  Note that Li-air batteries have 10-11 times the energy storage potential that Li-ion batteries do (per weight).  Zn-air batteries have about four times the energy storage potential as Li-ion batteries.  The potential or theoretical numbers are computed from the energy released from the metal assuming total oxidation from the oxygen.  It is clearly much greater than the energy released from the corresponding metal-air battery today; although this battery technology will improve over time.

This would address the weight and energy storage, but rechargeability is a problem.

Older lithium-air batteries do not have long lasting bi-functional cathodes where the oxygen reduction and evolution both take place.  Effective catalysts are needed to reduce the byproducts of the discharge, such as Li2O2 and Li2O.  These are not soluble in current electrolytes and eventually clog the pores of the cathodes, seizing the cell.  Membranes between the anode and cathode also can clog.  Similar problems occur for older zinc-air and other older metal-air batteries.  Thus to make effective (i.e. having a high rates of oxygen reduction and evolution) rechargeable metal-air batteries, new materials for cathode, catalysts for both the reduction and evolution cycles, electrolytes, and membranes are needed.

There are more problems uncovered by current research on Li-air.  Li-air batteries require more voltage to charge them than one obtains when using them.  This ratio is called “energy efficiency”, and most metal-air batteries today have energy efficiency around 60%.

Another problem is the discharge rate.  The reaction between lithium and oxygen in today’s Li-air batteries proceeds too slowly to generate significant current.  It is a little impractical to gang them up to get adequate current.

Next cost.  While current research tends to favor the performance of lithium-air batteries, zinc is a far more abundant metal than lithium, and hence the cost of zinc-air batteries could be significantly lower than that of lithium-air batteries.  At least two companies are headed in this direction with their zinc-air technologies.  One, ReVolt Technology, has a patented [2, 3] mixture of materials for the anode, cathode, catalyst, electrolyte, and membrane, and the other company, EOS Energy Storage, has a patent-pending mixture.  Both believe that their technologies can scale to utility sized batteries, i.e. batteries with tens to hundreds of MW/h of energy stored, and both believe that they can address the EV market (which would give them the scale to keep the price down at the utility level.)  In other words, both believe they have solved the above mentioned problems with today’s Li-air batteries.  The industry continues with considerable research being done by various organizations.  These organizations all hold a wide variety of related patents.  Lawyers will do well when the industry starts to shake out!

Of course, just as an array of wind or solar generators is needed to produce utility sized amounts of energy, an array of batteries is needed with a capacity sufficient to smooth out the peaks and valleys of the generated electricity.  E.g. the wind might not blow or the sun might not shine for several days in a row.  Allowing for these extremes could drive the cost of the batteries unacceptably high.  As a second level of backup, natural gas generators could also be part of the system, but one would expect very little natural gas to be burned over the course of the year with reasonably sufficient batteries.


[1] J.P.Zheng et al, J.Elec.Chem.Soc.155(6)A432-A437 (2008)

[2] Patent US 2007/0166602 A1, “Bifunctional Air Electrode”

[3] Patent US 2008/0096061 A1 “Metal-Air Battery or Fuel Cell”

CPV Environmental Impact



Today I read the paper “An Assessment of the Environmental Impacts of Concentrator Photovoltaics and Modeling of Concentrator Photovoltaic Deployment Using the SWITCH Model” June 2011 by Dr. Daniel Kammen of the Renewable and Appropriate Energy Laboratory at UC Berkeley and his Ph.D. students James Nelson, Ana Mileva, and Josiah Johnston.  [cf.]  It’s not too long (25 pages) and is packed with information.  I recommend it.  The review/summary here contains my comments.

The paper discusses, in the context of other forms of energy generation, the comparative environmental impact of CPV.  The short answer, if you don’t want to read any more, is that CPV has comparatively minimal environmental impact, and in particular is slightly worse than PV due to the former’s tracking system (see below) and a tiny bit better than CSP due to the latter’s cooling and water use.  Of course, oil, coal, and even natural gas are bad environmentally for a variety of reasons, and thankfully the paper doesn’t harangue about this too much.

The report considers three Life Cycle Assessment (LCA) phases: (1) fabrication and deployment of the energy generation facility, (2) energy production and maintenance, and (3) recycling and disposal at end of life of the facility.  Discussed in this context are the environmental issues of energy, emissions, water use, and land use.  Also considered in this report is the Energy Pay-Back Time (EPBT) which is the time (in years) that it takes to generate the net energy (roughly the energy generated minus energy used) in Phase 2 to be equal to the energy used in Phases 1 and 3, i.e. in creation and disposal of the generation facility.  Heretofore, this number has been estimated in the 3-15 year range; however, this report estimates it as less than 1 year for both PV and CPV. Caution:  one review of this paper that I read has challenged the logic and data used by the authors in their calculations of EPBT.  The authors point out that EPBT calculations are also sensitive to the geographic location of the generation facility, and hence have significant variance.

Green House Gas (GHG) emissions for Phase 1 are considered.  They are highest for large tracking systems such as CSP and CPV that use a lot of GHG-intensive steel in their structures. Such steel is heavy and incurs greater shipping costs in Phase 1.  Not only can the designs be improved to reduce the amount of steel used, but such steel could be manufactured where a large portion of the steel production energy came from solar or at least renewable energy sources.

Water use during Phase 1 is difficult to estimate due to lack of data on recycling, CPV use is estimated at 2 times that of PV.  Water use during operations, Phase 2, is significant since the large sites tend to be in water constrained regions.  In any case, for PV and CPV, water is only used for washing as opposed to CSP where it is used for wet cooling.  If dry cooling, i.e., air cooling, is used in a CSP plant, then water use is reduced 90% and is relegated to washing and steam production.

When mining, transportation, and disposal of non-renewable fuels are taken into consideration, the land use per GWh of renewable and non-renewable generations turns out to be comparable.  Hydroelectric and Wind are several times higher, and rooftop PV systems, where the land is already used by the building, are several times less. CPV has an advantage in land use over PV and CSP.  In addition, most large CPV and CSP systems are pole mounted, allowing potential reuse of most of the land under the arrays for plants and small animals.  Such use, it is noted by the authors, is not currently common; although CPV vendors seem to be leading here. Environmental impact studies should (by law) address impact on flora and fauna in the region; however, such studies can get around this by stating the impact is minimal in the large.

The authors also model CPV deployment in the southwest area covered by the Western Electricity Coordinating Council (WECC) by starting with around 1000 existing installations of various types and varying the mix of 10,000 additional renewable and conventional installations.  Their model runs thousands of wind and sun conditions on an hourly basis to meet the forecasted needs and to minimize the cost of generation, storage, and transmission.  The model uses NREL’s System Analysis Model (SAM) to get various costs of operation and maintenance.  At this point the paper is somewhat unclear as to just how the mix of the additional 10,000 generation types is determined.  It appears that CPV sites are preferentially added and CSP sites are not considered by this modeling.  That said, the conclusions are:

  • It would be economical to install between 12 and 43 GW of CPV by 2030 in the United States Desert Southwest
  • Including CPV allows for deeper CO2 reductions in the electric power system
  • CPV displaces natural gas generation on the margin
  • Strong carbon policy (e.g. charging $40/ton for CO2 generation) increases the deployment of CPV

Analyzing several of the graphs in this paper, it also appears that with the authors’ investment assumptions, the WECC area will need to increase its use of natural gas to cover peak usage.

In summary, I wish there were more studies like this.  Indeed, the authors’ model could be run many times over with differing investment assumptions to generate additional fascinating information.


Concentrated Solar Power (CSP)


Concentrated Solar Power (CSP)

The basic idea behind Concentrated Solar Power (CSP) is dead simple, especially if you liked to start fires with a magnifying glass when you were a kid:  Focus a lot of sunlight to gather heat, and use this heat to generate electricity.

There are several ways to do this.  A simple way, to get our mental juices flowing, would be to use the heat source to boil water to generate steam, and then use a steam engine to drive a generator to produce electricity.  While simple, this approach turns out to have a few problems, e.g., needing a water supply in the middle of a desert and the fact that steam is not a good energy storage medium.  Thus, sometimes this approach is used as a “back end” of a more complicated system, where one fluid is heated to a very high temperature, and this hot fluid is used to create steam for a steam engine.  This is discussed more below.

A vastly better approach is to focus the sun’s rays to create a very hot liquid, and to use it to heat a Stirling Engine to generate electricity.  The very hot liquid stays external to the Stirling Engine.  There is a nice article on Stirling Engines in Wikipedia here. Like steam engines, they are external combustion engines as opposed to internal combustion engines as are gasoline and diesel engines.  Here’s a picture from the Wikipedia article.  Since WordPress doesn’t support motion in gif files, you’ll have to click on the picture to see motion.

Stirling Engine

For this simple Stirling Engine, there is only one cylinder, hot at one end and cold at the other. A loose fitting displacer shunts the internal fluid between the hot and cold ends of the cylinder. A power piston at the end of the cylinder drives the flywheel, which in turn drives the generator.  In our case, our external hot fluid replaces the external “fire” in this picture.

Let’s break a CSP system down a little more.  There are several ways to “focus” the sunlight.  First there are three dimensional parabolic dishes that focus the light essentially onto the hot side of the Stirling Engine.  Here are some images taken from Google’s image collection (Click on them to see their original source.):

Above there is a single CSP with one Stirling Engine at the focal point, and below an array of such CSPs.

Note in this array there are multiple Stirling Engines. While more expensive, this is goodness, because the array keeps working in the presence of even multiple engine failures.

Another approach is for movable mirrors (heliostats) to reflect the sunlight to a “point” on a tower.  The mirrors are usually rather flat parabolic mirrors so that their focal point is quite far away – near the top of the tower.

In this tower/heliostat approach, the external fluid is heated at the top of the tower and piped down to a Stirling Engine or to a steam engine.  After it has been used for heating, the cooled external fluid is piped back to the tower to be reheated.

A second form of CSP uses a two dimensional parabolic trough:

Along the line of parabolic foci is a thermal collector pipe that not only serves as an “oven” for the heated fluid, but it also transports the heated fluid to a central generating facility.  Below is such a facility in Abu Dhabi, at one of the world’s largest CSP plants.

A third way to focus sunlight is with a Fresnel lens or mirror.  Recall these are used by many CPV systems as well.  In the lens case the thermal collector pipe is below the lens.  For Fresnel mirrors, it is above the mirrors. Here’s a photo:

The company Areva, has a fourth combination-type of setup.  Here are a couple photos from their web site:

The blue trough is a parabolic trough focusing the light onto the overhead “compact linear Fresnel reflector” which in turn focuses the light onto a thermal collector pipe.  Here’s a close-up photo of that:

To maximize efficiency, all CSP systems need tracking so that they “point” towards the sun.  The trough and Fresnel systems need only single axis tracking, while dual axis tracking is needed for tower/heliostat CSPs and also for parabolic dish arrays.

One potential problem CSP systems have is glare.  A system under construction in Cloncurry, Australia was scrapped in November 2010 due to concerns about reflective glare in an urban environment.

The next part of a CSP system is the external heating fluid, which is typically some sort of liquid salt, although other materials including super-heated steam and graphite have been used. The molten salt is a mixture of 60 percent sodium nitrate and 40 percent potassium nitrate, commonly called saltpeter. New studies show that calcium nitrate could be included in the salts mixture to reduce costs and with technical benefits. This salt melts at 220 °C (430 °F) and is kept liquid at 290 °C (550 °F) in an insulated storage tank.   The main feature of liquid salt is that it can be heated to very high temperatures, in excess of 500 °C, and at this heat, it can be used to drive a Stirling Engine or generate steam for many hours after the sun goes down.  This time of course depends on the initial temperature, the quantity of liquid, the insulation, and the efficiency of the Stirling or steam engine used.  Typically current systems continue to generate significant amounts of electricity for 7 to 8 hours after the CSP stops heating the salt.  This isn’t quite enough for 24 hour operation, and some utility companies set up “hybrid” systems where the load at night is met with a gas fired generator.

These systems are improving, and the 19.9 MW CSP system in Andasol, Spain generated 24 hours of continuous electricity in July 2011 using a molten salt storage system.  This design should average 20 hours per day of electrical power generation, hitting 24 hours on particularly sunny summer days.  This plant has a field of 2650 heliostats that focus sunlight on a central tower. Here’s a photo:

Future posts will compare CSP systems with CPV systems for efficiency and cost effectiveness.


Storing Energy from Solar Arrays


Storing Energy from Solar Arrays

Even in the case there is heavy daytime use for solar power, e.g. air conditioning, there will always be a need for power when the sun can’t provide it.  Ideally, the solar generation system will be over-specified so that peak usage can be handled, in which case there is a need to store the excess energy for “after sun” hours.  In addition, peak energy consumption is in the afternoon, and solar arrays are effective in the morning hours, which might generate excess power in the mornings.

Now the best “storage” device is usually the grid.  Dump your excess energy onto the grid so that someone else can use it, and then use the grid whenever (day or night) your solar power isn’t adequate.

The problem is that the grid has only minuscule renewable storage capacity – most of it behind dams that contain hydro-electric generators. Thus “storing” excess energy on the grid assumes that someone can use it at essentially that moment.  Utility companies try to shape demand by turning on and off not only hydro-electric generators, but also (ugh) fossil fuel generators and by adjusting the various components of energy pricing.  For the excess producer of solar or other renewable energy, this means that putting electricity onto the grid at non-peak times, may provide low or even negative prices for that energy.

That said, what if you can’t (or don’t want to) dump your excess power onto the grid for some reason?  Here are some thoughts to be elaborated on in subsequent postings:

  • Store the energy as heat, e.g. as hot water.  This can be done in hot water tanks, or even in a swimming pool.  A more sophisticated method is to store the heat in a heat sink such as molten salt (very hot), which can be reused in various ways.  There are various salts besides NaCl – common table salt – but the idea is to heat the salt to over 500 degrees Celsius.  Well insulated, liquid salt can keep 90% of its heat for over 24 hours.
  • Storing heat in gravel has merit.  Isentropic’s Pumped Heat Electricity Storage (PHES) system is based on the First Ericcson cycle and uses a heat pump to store electricity in thermal form. The storage system uses two large (7m high  x 8m in diameter) containers of gravel, one hot (500C) and one cold (-150C) with a heat pump machine between them. Electrical power is input to the machine which compresses/expands air to 500C on the hot side and -150C on the cold side. The air is passed through the two piles of gravel, where it gives up its heat/cold to the gravel. In order to regenerate the electricity, the cycle is reversed with a round trip efficiency of 70-80 percent. The temperature difference is used to run the system as a heat engine.
  • Compressed Air Energy Storage (CAES) is very interesting; however,  don’t think of a tank of compressed air, but rather think of an underground cavern filled with it.  In the middle of the night when the price of electricity is low, utilities can run compressors and pump air into a cavern at around 750 psi.  When the price of electricity goes up, the compressed air is then used to power a turbine generator. Often this portion of the design is supplemented by the use of natural gas either to heat the air or to mix with the pressurized air to burn.  Investigations by EPRI indicate that up to 80 percent of the U.S. has geology suitable for CAES. A single 300 megawatt CAES plant would require 22 million cubic feet of storage space — enough to store eight hours’ worth of electricity. Ridge Energy has a nice diagram here. Whether CAES systems can be commercially viable at a utility level remains to be seen.  One negative argument is here.
  • Store it as kinetic energy, e.g. in a fly wheel.  Well, there are horror stories of large fly wheels disintegrating with hunks flying around causing much damage.  Not a pretty picture.  Fly wheels in general lose a lot of energy to friction, and really are only good to transition use from one source of energy to another.  Lots of small fly wheels are too expensive to maintain. The company Velkess (founded 2007) is developing new flywheel technology.  Keep an eye on them.
  • Pump water up hill.  This isn’t as silly as it sounds, especially if what is needed is water pressure.  Think of those old fashioned city water tanks, which are decidedly useful. On a large scale, filling a reservoir that was above a hydro-generation facility would be a good idea.  For example, the TVA’s Racoon Mountain pump-up facility has been operating for a number of years.  Some estimate that about 10% of the hydro-electric dams are suitable for this.
  • Freeze water.  If you don’t have enough use for ice, e.g., for cooling, then run the freezer during the day and let it “coast” at night.  Some commercial refrigerators have logic for this, expecting both power and usage to be nil at night and to start up in the morning.  Even when commercial electricity costs less at night, this is a win for solar.  For wind, making ice at night and using it to cool a building during the day is done by CALMAC.
  • Use electrolysis to make hydrogen, then burn the hydrogen later to make electricity.  This approach is costly, and it takes considerable energy to compress the hydrogen into a liquid form so that it can be shipped or stored easily.
  • A more sophisticated version of the preceding is to use electrolysis to make MgH2 – magnesium hydroxide.  This is a relatively stable liquid, and the hydrogen can be released either by mixing the MgH2 with water or by heating it.  The released hydrogen can then be burned to make electricity.  The byproduct after adding water, Mg(OH), is essentially Milk of Magnesia. which can be recycled to recover the magnesium and start the process all over again. In addition to storing energy in the form of hydrogen, this “liquid energy” and its byproduct can be transported easily in trucks, boats, etc..
  • Of course batteries are the standard answer, and battery technology is getting better every year.  Here, you get a little extra mileage bypassing the inverter(s) and using DC appliances, but I’m not sure what the trade-offs are.  For example, using LED’s for DC lighting would be a good idea.  It is pretty easy to bypass the power supplies in most computer equipment.  DC fans would work.  But the cost of DC ovens, air conditioners, etc. is probably prohibitive.  At the scale of utilities, EOS Aurora and Revolt Technology both claim to have rechargeable Zinc-Air batteries that will scale hold 6 MWh each.  Zinc-air batteries aren’t as good as Lithium-air, but they are vastly cheaper.  The battery researchers are lately hot on Vanadium Redox batteries which you can read about here.

As I’ve thought about putting solar arrays on my house’s rooftop, some of the above ideas may work for me, e.g. heating water, and getting the freezer and refrigerator extra cold during the day.  On the other hand, I’ll also connect to the grid and take the pittance that the electric company gives me for my “donations.”

Finally, for you wind farm fans, most of these ideas apply – with the exception of storing liquid salt.  Not that a wind mill can’t make liquid salt, but solar arrays essentially start there.